Glen-L.com

Hello all,

I have ordered my plans for the Rogue Runner at Glen L. I would really like to power it with a jet ski. The plans say 40-125 hp. for power rating. Not finding much info on converting cc rating to hp rating for a donor ski.

I also came across a full size jet pump and a mercuiser 4 cyl. that I could mate up if the jet ski option isnt as viable as it appears.

Also looking for you guys that have already done this type of power.


Thanks, Chris

Let the fun begin. Today was great. My Wife was working out of town all week and got home. Waited all day watching the UPS tracking of my plans. Finally got here about 6 pm. Was worried they might wait until next week. That would have been bad! On top of the plans showing up, I found a donor ski today. Not exactly what I was looking for, but I think it will be okay.

The guy that does the repairs on our work trucks had this 951.2 cc jetski on a like new trailer. It is complete and looks pretty nice. Almost too nice to cut up, almost........ The Rotax is toast but all there. Not only does it have the pump and all the other parts I need, the extras can be sold, including the trailer, seat, carbs etc. I will use the guages and all the controls I think. All for $100.00. The pump even has a trim on it with a switch on the dash. That seems to be a good feature to have?

This will drive me to get the shop done faster! Off to the lumber store in the morning.

It looks like a good utility hull. Keep us posted.. And as always while some of us are word challenged, we all do well with pictures.

There is no standard math conversion to figure horsepower based on CC's or cubic inches.

In particular, jet ski mfg's squeeze un-godly amounts of horsepower out of very tiny displacement engines - upwards of 3 horses per cubic inch (1 cubic inch = 16.4 cc's (rounded)), while a standard gas powered marine engine whether outboard or inboard is close to 1 horse per cubic inch (give or take a tiny bit).

That 951.2 cc you note would be about 58 cubic inches. In an outboard that would be a 50 or 60 horse - I suspect that particular motor is at least rated at double that.

When comparing a jet to an outboard (or inboard or I/O) when both have the same Brake horsepower (BHP), the jet will suck in the low end torque department (in comparison) and you often need upwards of 30% greater BHP horsepower with a jet to get the same top end speed as the (conventional) drives require - which means you burn more gas to get the same result. (a 90 horse Merc outboard produces about 100 horses at the crank - when you stick on a jet lower unit, it's sold as a "60 Jet" - so the equivalent of 60 horses at the (prop) but still 100 horses at the crank).

However, jet's definately have the "cool factor" and they can run in a shallow puddle without hanging up on the bottom.

Their one other downfall, due to the high horse/displacement output is a very short lifespan in comparison to other options. BRP who probably leads the engineering only suggests a 10 year lifespan for the engines - and that's 10 years total life, not 10 years before rebuild. I asked the rep at a boatshow about that "advertisement" and he stated that if the motor is used an average of 100 hours per year it will generally require a rebuild every 300-400 hours (3-4 years), so by about year 10 when it goes for the third time it's no longer worth rebuilding.

Think of them like an Indy car - the engine puts out about a zillion horsepower - but after one or two training runs and a single race, the motor is torn down and rebuilt.

I'm not trying to crap all over jet drives, they definately have their place, but it's worth doing some investigating before selecting one as your power option because just about ever other option will be longer lived and cost less to run...

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

You are right. The 951cc is rated at 135 hp. Also, I talked to a couple dealers that also rent PWC and they said the same thing about BRP's. They dont rent them any more for that engine failure reason. I was looking at the jet option for a couple reasons. #1, the Willamette river is 3/4 of a mile from my house and can get pretty shallow. I also fish the mouth at Portland where its deep enough to take tankers and other deep draft ships.

#2 is cost. I just went through rebuilding my big boat. Marinzed VW TDI's inboard. The transmissions are 2500.00 each. The jet has no transmission in my use. I was wanting to see what I could produce with quality and spending as little as possible.

I dont have a problem bagging the Ski, and putting, say a Berkley/inboard, maybe even diesel for that one if I go that route. was just studyong my plans. It shows a 750 lb. limit for engine/pump variation.

It sounds like you have done you "homework" and are considering a jet for good reasons. I get alot of questions about jets on another board that I write for and many are under the mistaken impression that jets are just so much faster than other options and are quite shocked to find that horse for horse they are practically the slowest thing out there and tend to burn more gas in the process.

They really do have their place, it's just the "average boater" has little need of one - but for river running they are ideally suited..

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

Got the first installment of lumber and plywood yesterday. 6 sheets of marine ply and 100+ bd. ft. of mahogany.

That's too "pretty" to cut up. Better grab a beer and a lawnchair and just look at it for a while before you get the saw out

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

Yeah, that is like cutting thin little strips out of 100 dollar bills but you won't be able to tape them back together ~!~

Good luck~

Steve

This boat is progressing into more than I planned. Im going to extend it to the approved 20'. I also think I will save the jetski for a lighter stitch and glue version. This one will be over 800 lbs before rigging, gear and passengers. May still find a jet outboard, but budget will dictate that. Before when I was looking for jet skis, I found tons of Berkley pumps cheap. Now, that I could use one, none under 900.00. I will still watch, but for sanity sake, I will plan on an outboard.


Ideas? Should I move it to another category?

Thanks, Chris

Sure, start a new thread in powerboats

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

HP alone is useless when dealing with a jet drive. Not to mention, PWC builders seem to make the numbers up to suit their advertising needs.

20', and all that weight with a PWC drive? Well, you won't need a speedometer! A calendar, yes, a speedometer, not so much. That hull would be decent with a high-mass drive, like the hamilton, or the old jacuzzi YJ drive, but a small pump would be a disappointment.

Shallows and a piece-of-crap berk pump... you are going to get really familiar with feeler-gauges, and impeller shims! Any mixed flow is not something you want to pump ditches with. one tiny little 3/16" pebble can destroy the pump, leaving you needing a new impeller (360.00USD for a cheapo cast imp) and a new wear-ring (90.00USD) One of Duane's polymer rings will save you some damage, but it's still got the potential to cost! A bigger stone usually goes through the impeller, then shatters the back of the blades when it lodges against the bowl vanes. It vibrates like something from an "adult" store... then damages the tail bushing. Those "cool" jet boats you see racing in some ditch in NZ will almost exclusively have Hamilton pumps-not the best for speed, but they would pump a pond full of buckshot 'n beer bottles and keep going.

Jets suck in the low end??? Have you ever even had any jet drive??? HP to HP jets will holeshot any similar prop in a big way. There is a ram-effect to consider, never the less, a jet will produce nearly the same thrust in a dead-stop condition, as they will when the hull is moving at top speed. (and why there are so many commercial heavy transports using jets over props) There is significantly less drag at high speed. Theoretically, a jet pump can produce better fuel economy than a screw. None of the energy is spent slinging water radially, there is no transmission loss, and it's efficiency is not changed by angle of attack. In practice, mass-produced pumps with rough castings, internally leaky pumps, too much intake/not enough intake area, and just plain the wrong pumps, wrong nozzles, make for horrible economy. Proper matching, and setup are a must. It's harder than just bolting a new screw on.

Short life? Depends more on a properly maintained engine than drive line. lifespan=cool/not cold oil changed often, multiple filters, moly rings, and correct clearances. Again, build it right, and it lasts, build it wrong, and do it again.

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

How much of the jet issue is Ford vs. Chevy type of disscussion? The reason I ask, is there are tons of Berkeley pumps out there and only one or two Hamiltons in all of Ebay and Craigslist. Some of that can be explained by price, and there were lots od Berkeleys put in glass boats that rot out. Out here, the Hamiltons seem to be in the very high end aluminum sleds.

I found a pair of Berks yesterday. He said I can have both for $500. I only want one though. A complete rebuild kit is $600. I got a boat from a guy at work with a rebuilt Buick (paperwork) for $500. The transom and sole are soft. But trailer, new bilge pump, fuel tank and the engine system for $500, pump and rebuild kit for $850. I cant find much of an outboard for $1500 and Im getting the extras with it. And the plus and minus of having a jet too though.

So many options to weed through.

So today I went by the machine shop to pick up some parts for work. I was talking to one of the fabricators about my project. He reccomends using the jet ski pump rather than the Berkley.

Now the JS runs about 6800rpms and my inboard ( a 120 or a 165 Mercruiser) engine would run about 4K WOT? He suggested a gearbox to make up the difference. Now I know I do that on my wood lathe, but can it be that simple? I stopped by the bearing store and the guy just threw up hs hands, saying I have to have an engineer tell him what I need.

The JS wouldnt be as efficient running the lower rpm's, but am I just losing the top speed? I dont need to go 50mph+

Chris

Hi Chris,

The lumber looks great! I haven't purchased any for my Belle Isle project yet, so I'm curious where you got it. Will you share that info?

Thanks.

Bob (in Corvallis)

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I'm gonna build me a boat with these two hands
It'll be a fair curve from a noble plan
let the chips fall where they will cause
I've got boats to build
>> From Guy Clark "Boats To Build" - Asylum Records 1992